This application relates to a displacement sensor utilizing a Hall effect sensor and a magnet, wherein the travel of the Hall effect sensor is non-parallel to an axis between the poles of the magnet, extending the range of the displacement sensor.
One known type of displacement sensor includes a Hall effect sensor placed adjacent to a magnet. The Hall effect sensor and the magnet are attached to different objects. The two objects move relative to each other, and the Hall effect sensor, by sensing the relative position of the magnet, can determine the amount of relative movement of the objects.
Such displacement sensors have had limited application in that there is typically a limited distance range which can be measured. As an example, typical production Hall effect displacement sensors are able to measure approximately 0.25″ of movement.
For many applications, the Hall effect sensor and its 0.25″ range would be insufficient. One example is a displacement sensor for sensing the amount of movement of a piston in a disc brake due to friction surface wear. As known, a brake actuator drives a pair of pistons in a disc brake, and the pistons force a brake pad against a rotating component, slowing rotation of the rotating component. There is normal wear on the brake pad, and typically a disc brake piston is provided with an adjustment mechanism. The adjustment mechanism has historically included a mechanical linkage that senses the total movement, and adjusts the piston relative to a tappet gear to take up clearance. Typically, there is a desired amount of piston movement, and with wear on the brake pad, the piston needs to move an amount beyond this desired amount. Thus, the adjustment mechanism changes a rest, or starting position of the piston such that it only needs to move the desired amount, even with wear on the brake pad.
More recently, electric motors have been developed for replacing the mechanical linkage in the adjustment mechanism. An electric motor typically drives a gear, that in turn will drive the tappet gears to adjust the pistons.
Such an electric motor adjustment mechanism would benefit from feedback of the amount of necessary adjustment. Thus, some sensor for sensing the amount of movement of the pistons is desirable. The limited range provided by the current Hall effect displacement sensors is inadequate for this application. On the other hand, in the vicinity of the disc brake and its pistons, there is limited available space. For this reason, the relatively small Hall effect sensor would be quite desirable.